gokselk opened a new pull request, #13770:
URL: https://github.com/apache/datafusion/pull/13770
## Which issue does this PR close?
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Closes #13769.
## Rationale for this change
The current implementation of `with_reorder` discards all existing ordering
information when applying a new ordering. This is overly conservative since in
many cases, parts of the existing ordering remain valid and could be preserved.
Preserving valid orderings is important for query optimization as it allows the
optimizer to avoid unnecessary sorting operations.
## What changes are included in this PR?
1. Enhanced `with_reorder()` to preserve valid suffixes from existing
orderings when they don't conflict with the new ordering
2. Added filtering of constant expressions from ordering considerations
3. Added `exprs_equal()` helper method to `EquivalenceGroup` for comparing
expressions considering equivalence classes
4. Added comprehensive test suite covering:
- Constant expression filtering
- Suffix preservation
- Equivalent expression handling
- Incompatible prefix cases
- Complex scenarios combining multiple features
## Are these changes tested?
Yes, the PR includes extensive test coverage:
- `test_with_reorder_constant_filtering`: Tests filtering of constant
expressions
- `test_with_reorder_preserve_suffix`: Verifies preservation of valid
ordering suffixes
- `test_with_reorder_equivalent_expressions`: Tests handling of equivalent
expressions
- `test_with_reorder_incompatible_prefix`: Ensures proper handling of
incompatible orderings
- `test_with_reorder_comprehensive`: Tests complex interactions between
constants, equivalences, and multiple orderings
## Are there any user-facing changes?
This change is an internal optimization that preserves more ordering
information. While there are no direct API changes, users may notice improved
query performance in scenarios where ordering information is better preserved
through operations that modify sort orders.
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